Four groups of rats (n=10/group) have been studied at 4 different doses of carbamazepine . . . 0, 2.25, 5.0 and 9.0 g/kg for up to 21 days. Plasma was obtained for quantitation of both the parent compound and its 10,11 epoxy metabolite which were measured using a HPLC procedure that employs a UV detector. In vitro binding studies were also carried out with an adenosine agonist (CHA) and an antagonist (DPX). Based on in vitro binding data and plasma levels of the parent compound, it was concluded that chronic carbamazepine treatment increases brain adenosine receptors in rats.